SC16C652 datasheet(11/41 Pages) PHILIPS

11 / 41 page

Philips Semiconductors

SC16C652

Dual UART with 32 bytes of transmit and receive FIFOs

Product data

Rev. 04 — 20 June 2003

11 of 41

9397 750 11634

6.8 Programmable baud rate generator

The SC16C652 supports high speed modem technologies that have increased input

data rates by employing data compression schemes. For example, a 33.6 kbit/s

modem that employs data compression may require a 115.2 kbit/s input data rate.

A 128.0 kbit/s ISDN modem that supports data compression may need an input

data rate of 460.8 kbit/s. The SC16C652 can support a standard data rate of

921.6 kbit/s.

A single baud rate generator is provided for the transmitter and receiver, allowing

independent TX/RX channel control. The programmable Baud Rate Generator is

capable of operating with a frequency of up to 80 MHz. To obtain maximum data rate,

it is necessary to use full rail swing on the clock input. The SC16C652 can be

conﬁgured for internal or external clock operation. For internal clock oscillator

operation, an industry standard microprocessor crystal is connected externally

between the XTAL1 and XTAL2 pins. Alternatively, an external clock can be

connected to the XTAL1 pin to clock the internal baud rate generator for standard or

custom rates (see Table 6).

The generator divides the input 16

× clock by any divisor from 1 to 216 − 1. The

SC16C652 divides the basic external clock by 16. The basic 16

× clock provides table

rates to support standard and custom applications using the same system design.

The rate table is conﬁgured via the DLL and DLM internal register functions.

Customized Baud Rates can be achieved by selecting the proper divisor values for

the MSB and LSB sections of baud rate generator.

Programming the Baud Rate Generator Registers DLM (MSB) and DLL (LSB)

provides a user capability for selecting the desired ﬁnal baud rate. The example in

Table 6 shows the selectable baud rate table available when using a 1.8432 MHz

external clock input.

Fig 3.

Crystal oscillator connection.

002aaa169

1.8432 MHz

22 pF

47 pF

1.8432 MHz

47 pF

100 pF

1.5 k

Ω

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